Synthetic Biology relies on the ability to build novel DNAs from component parts. Double strand (ds) DNA molecules have been assembled by creating staggered ends at the both ends of a first DNA duplex. This has been achieved using restriction endonucleases or by using exonuclease digestion or by T4 DNA polymerase followed by hybridization and optional ligation of a second DNA duplex to the first duplex. Techniques that utilize exonucleases and ligases in a reaction mixture also specify the use of non-strand displacing polymerases.